Based on the article, which best replaces the question mark in the diagram above?

Which of the following is a complex sentence? a. after henry submitted his essay, he realized that he hadn't proofread the last page. b. identity theft is a growing problem, especially among seniors. c. we didn't have enough potatoes for dinner, so we served rice instead. d. jim tried to watch a video on a device connected to a crowded wireless network; as a result, the video stuttered and froze.